On Windows if geventmp is present gpython startup fails:

    (1.wenv) Z:\home\kirr\src\tools\go\pygo-win\pygolang>gpython
    Traceback (most recent call last):
      File "C:\Program Files\Python310\lib\runpy.py", line 196, in _run_module_as_main
        return _run_code(code, main_globals, None,
      File "C:\Program Files\Python310\lib\runpy.py", line 86, in _run_code
        exec(code, run_globals)
      File "Z:\home\kirr\src\tools\go\pygo-win\1.wenv\Scripts\gpython.exe\__main__.py", line 7, in <module>
      File "Z:\home\kirr\src\tools\go\pygo-win\pygolang\gpython\__init__.py", line 450, in main
        pymain(argv, init)
      File "Z:\home\kirr\src\tools\go\pygo-win\pygolang\gpython\__init__.py", line 223, in pymain
        init()
      File "Z:\home\kirr\src\tools\go\pygo-win\pygolang\gpython\__init__.py", line 428, in init
        _ = monkey.patch_all(thread=patch_thread)      # XXX sys=True ?
      File "Z:\home\kirr\src\tools\go\pygo-win\1.wenv\lib\site-packages\gevent\monkey.py", line 1255, in patch_all
        _notify_patch(events.GeventWillPatchAllEvent(modules_to_patch, kwargs), _warnings)
      File "Z:\home\kirr\src\tools\go\pygo-win\1.wenv\lib\site-packages\gevent\monkey.py", line 190, in _notify_patch
        notify_and_call_entry_points(event)
      File "Z:\home\kirr\src\tools\go\pygo-win\1.wenv\lib\site-packages\gevent\events.py", line 105, in notify_and_call_entry_points
        subscriber(event)
      File "Z:\home\kirr\src\tools\go\pygo-win\1.wenv\lib\site-packages\geventmp\monkey.py", line 160, in _patch_mp
        _patch_module("_mp.3._mp_util", _patch_module=True, _package_prefix='geventmp.')
      File "Z:\home\kirr\src\tools\go\pygo-win\1.wenv\lib\site-packages\geventmp\monkey.py", line 121, in _patch_module
        gevent_module = import_module(_package_prefix + name)
      File "C:\Program Files\Python310\lib\importlib\__init__.py", line 126, in import_module
        return _bootstrap._gcd_import(name[level:], package, level)
      File "<frozen importlib._bootstrap>", line 1050, in _gcd_import
      File "<frozen importlib._bootstrap>", line 1027, in _find_and_load
      File "<frozen importlib._bootstrap>", line 1006, in _find_and_load_unlocked
      File "<frozen importlib._bootstrap>", line 688, in _load_unlocked
      File "<frozen importlib._bootstrap_external>", line 883, in exec_module
      File "<frozen importlib._bootstrap>", line 241, in _call_with_frames_removed
      File "Z:\home\kirr\src\tools\go\pygo-win\1.wenv\lib\site-packages\geventmp\_mp\3\_mp_util.py", line 16, in <module>
        from gevent.os import _watch_child
    ImportError: cannot import name '_watch_child' from 'gevent.os' (Z:\home\kirr\src\tools\go\pygo-win\1.wenv\lib\site-packages\gevent\os.py)

That happens because geventmp does not support windows actually.

-> Fix it by requiring geventmp to be present only on non-windows.

Adjust related comment as https://github.com/karellen/geventmp/pull/2 has been merged long ago.

On windows setuptools install gpython.exe and gpython-script.py while
pip/distlib install gpython.exe with gpython-script sometimes embedded
into gpython.exe itself with argv[0] pointing to 'gpython' without .exe
suffix. This leads to gpython startup failure:

    (1.wenv) Z:\home\kirr\src\tools\go\pygo-win\pygolang>gpython
    Traceback (most recent call last):
      File "C:\Program Files\Python310\lib\runpy.py", line 196, in _run_module_as_main
        return _run_code(code, main_globals, None,
      File "C:\Program Files\Python310\lib\runpy.py", line 86, in _run_code
        exec(code, run_globals)
      File "Z:\home\kirr\src\tools\go\pygo-win\1.wenv\Scripts\gpython.exe\__main__.py", line 7, in <module>
      File "Z:\home\kirr\src\tools\go\pygo-win\pygolang\gpython\__init__.py", line 437, in main
        pymain(argv, init)
      File "Z:\home\kirr\src\tools\go\pygo-win\pygolang\gpython\__init__.py", line 79, in pymain
        if not _is_buildout_script(exe):
      File "Z:\home\kirr\src\tools\go\pygo-win\pygolang\gpython\__init__.py", line 442, in _is_buildout_script
        with open(path, 'rb') as f:
    FileNotFoundError: [Errno 2] No such file or directory: 'Z:\\home\\kirr\\src\\tools\\go\\pygo-win\\1.wenv\\Scripts\\gpython'

    (1.wenv) Z:\home\kirr\src\tools\go\pygo-win\pygolang>dir ../1.wenv/scripts/gpython*

    Directory of Z:\home\kirr\src\tools\go\pygo-win\1.wenv\scripts

    26.04.2023     14:17       108,404  gpython.exe
           1 file                   108,404 bytes
           0 directories     88,508,866,560 bytes free

-> Adjust pymain to handle this case accordingly.

On windows upon terminating signal reception exict code of the process
is always 3 instead of -signo. And so test_signal_all was failing as

        def test_signal_all():
            retcode, out, _ = _pyrun([dir_testprog + "/signal_test_all.py"], stdout=PIPE)
            assert b"ok (notify)"        in out
            assert b"ok (ignore)"        in out
            assert b"terminating ..."    in out
    >       assert retcode == -syscall.SIGTERM.signo
    E       assert 3 == -15
    E        +  where 15 = os.Signal(15).signo
    E        +    where os.Signal(15) = syscall.SIGTERM

- There is no e.g. signal.SIGKILL on windows:

    golang/os/signal_test.py::test_signal_all Traceback (most recent call last):
      File "Z:\home\kirr\src\tools\go\pygo-win\pygolang\golang\os\testprog\signal_test_all.py", line 82, in <module>
        main()
      File "Z:\home\kirr\src\tools\go\pygo-win\pygolang\golang\os\testprog\signal_test_all.py", line 39, in main
        allsigv.remove(syscall.SIGKILL) # SIGKILL/SIGSTOP cannot be caught
    AttributeError: module 'golang.syscall' has no attribute 'SIGKILL'. Did you mean: 'SIGILL'?

  -> filter-out signals conditionally depending on their presence.

- Need to also filter-out SIGILL/SIGABRT because upon reception MSVC
  runtime terminates process.

Because on Windows os.kill unconditionally terminates target process,
even if own self, instead of sending it any kind of signal.

We use SIGUSR1/SIGUSR2 mainly in this test, but those signals are not
available on Windows:

        @func
        def test_signal():
            # Notify/Stop with wrong chan dtype -> panic
            _ = panics("pychan: channel type mismatch")
    >       with _:  signal.Notify(chan(2), syscall.SIGUSR1)
    E       AttributeError: module 'golang.syscall' has no attribute 'SIGUSR1'

-> Use SIGTERM/SIGINT if SIGUSR1/SIGUSR2 are not available.

Don't want to use SIGTERM/SIGINT unconditionally because those signals are
better to leave for the job control so that e.g. nxdtest can properly kill
spawned pygolang tests.

On Windows in text mode files are opened with encoding=locale.getdefaultlocale()
which is CP125X instead of UTF-8 even if $PYTHONIOENCODING=UTF-8. This
way e.g. test_strings_print fail as:

    E           Failed: not equal:
    E           Expected:
    E               print(qq(b)): "привет αβγ b"
    E               print(qq(u)): "привет αβγ u"
    E           Got:
    E               print(qq(b)): "привет αβγ b"
    E               print(qq(u)): "привет αβγ u"

where "Expected" was read from golang/testprog/golang_test_str.txt and
decoded wrongly.

-> Fix it by always opening files for reading in binary mode and
utf8-decoding manually, if needed, everywhere.

golang: tests: Spawn subprocess python with $PYTHONIOENCODING set to encoding of stdin/stdout/stderr

We need to do it because on Windows `python x.py | ...` runs with stdio
encoding set to cp125X even if just `python x.py` runs with stdio
encoding=UTF-8.

    (1.wenv) Z:\home\kirr\src\tools\go\pygo-win\pygolang\golang\testprog>python golang_test_str.py
    print(qq(b)): "привет b"
    print(qq(u)): "привет u"

    (1.wenv) Z:\home\kirr\src\tools\go\pygo-win\pygolang\golang\testprog>python golang_test_str.py |more
    print(qq(b)): "яЁштхЄ b"
    print(qq(u)): "яЁштхЄ u"

    (1.wenv) Z:\home\kirr\src\tools\go\pygo-win\pygolang\golang\testprog>python golang_test_str.py >aaa.txt
    (1.wenv) Z:\home\kirr\src\tools\go\pygo-win\pygolang\golang\testprog>type aaa.txt
    print(qq(b)): "яЁштхЄ b"
    print(qq(u)): "яЁштхЄ u"

Which leads to the following test_strings_print failure:

    E           Failed: not equal:
    E           Expected:
    E               print(qq(b)): "привет b"
    E               print(qq(u)): "привет u"
    E           Got:
    E               print(qq(b)): "������ b"
    E               print(qq(u)): "������ u"

We also change golang_test_str.py to print not only russian and english
letters, but also greek ones. This is to make sure that stdout IO encoding would
not go cp125X unnoticed because then printing will fail with UnicodeEncodeError.

Note: in the above example both got and expected are wrong. Via
$PYTHONIOENCODING we only fix "got" and we will fix "expected" in the followup
patch. After current patch test_strings_print result is

    E           Failed: not equal:
    E           Expected:
    E               print(qq(b)): "привет αβγ b"
    E               print(qq(u)): "привет αβγ u"
    E           Got:
    E               print(qq(b)): "привет αβγ b"
    E               print(qq(u)): "привет αβγ u"

Apparently on Windows pytest detects terminal width differently than on
Linux/macOS and the test fails as

    E           Failed: not equal:
    E           Differences (unified diff with -expected +actual):
    E               @@ -1,5 +1,12 @@
    E               -...
    E               -_____________________________________ main _____________________________________
    E               -../__init__.py:...: in _
    E               +============================= test session starts =============================
    E               +platform win32 -- Python 3.10.11, pytest-7.3.1, pluggy-1.0.0
    E               +rootdir: PYGOLANG
    E               +collected 1 item
    E               +<BLANKLINE>
    E               +golang_test_defer_excchain.py F                                          [100%]
    E               +<BLANKLINE>
    E               +================================== FAILURES ===================================
    E               +____________________________________ main _____________________________________
    E               +../__init__.py:106: in _
    E                    return f(*argv, **kw)
    E                golang_test_defer_excchain.py:42: in main
    E               @@ -8,6 +15,6 @@
    E                <BLANKLINE>
    E                During handling of the above exception, another exception occurred:
    E               -../__init__.py:...: in __exit__
    E               -    ...
    E               +../__init__.py:183: in __exit__
    E               +    d()
    E                golang_test_defer_excchain.py:31: in d1
    E                    raise RuntimeError("d1: aaa")
    E               @@ -15,9 +22,9 @@
    E                <BLANKLINE>
    E                During handling of the above exception, another exception occurred:
    E               -../__init__.py:...: in __exit__
    E               -    ...
    E               +../__init__.py:183: in __exit__
    E               +    d()
    E                golang_test_defer_excchain.py:33: in d2
    E                    1/0
    E               -E   ZeroDivisionError: ...
    E               +E   ZeroDivisionError: division by zero
    E                <BLANKLINE>
    E                During handling of the above exception, another exception occurred:
    E               @@ -25,3 +32,5 @@
    E                    raise RuntimeError("d3: bbb")
    E                E   RuntimeError: d3: bbb
    E               -=========================== ...
    E               +=========================== short test summary info ===========================
    E               +FAILED golang_test_defer_excchain.py::main - RuntimeError: d3: bbb
    E               +============================== 1 failed in 1.45s ==============================

-> Fix it by not requesting header to be of particular width.

On windows print emits \r\n instead of just \n. Here is how e.g.
test_defer_excchain_dump fails without normalization:

    E           Failed: not equal:
    E           Differences (unified diff with -expected +actual):
    E               @@ -1,42 +1,43 @@
    E               -Traceback (most recent call last):
    E               -  File "PYGOLANG/golang/__init__.py", line ..., in _
    E               -    return f(*argv, **kw)
    E               -  File "PYGOLANG/golang/testprog/golang_test_defer_excchain.py", line 42, in main
    E               -    raise RuntimeError("err")
    E               -RuntimeError: err
    E               -<BLANKLINE>
    E               -During handling of the above exception, another exception occurred:
    E               -<BLANKLINE>
    E               -Traceback (most recent call last):
    E               -  File "PYGOLANG/golang/__init__.py", line ..., in __exit__
    E               -    ...
    E               -  File "PYGOLANG/golang/testprog/golang_test_defer_excchain.py", line 31, in d1
    E               -    raise RuntimeError("d1: aaa")
    E               -RuntimeError: d1: aaa
    E               -<BLANKLINE>
    E               -During handling of the above exception, another exception occurred:
    E               -<BLANKLINE>
    E               -Traceback (most recent call last):
    E               -  File "PYGOLANG/golang/__init__.py", line ..., in __exit__
    E               -    ...
    E               -  File "PYGOLANG/golang/testprog/golang_test_defer_excchain.py", line 33, in d2
    E               -    1/0
    E               -ZeroDivisionError: ...
    E               -<BLANKLINE>
    E               -During handling of the above exception, another exception occurred:
    E               -<BLANKLINE>
    E               -Traceback (most recent call last):
    E               -  ... "PYGOLANG/golang/testprog/golang_test_defer_excchain.py", line 45, in <module>
    E               -    main()
    E               -  ...
    E               -  File "PYGOLANG/golang/__init__.py", line ..., in _
    E               -    with __goframe__:
    E               -  File "PYGOLANG/golang/__init__.py", line ..., in __exit__
    E               -    ...
    E               -  File "PYGOLANG/golang/__init__.py", line ..., in __exit__
    E               -    ...
    E               -  File "PYGOLANG/golang/__init__.py", line ..., in __exit__
    E               -    ...
    E               -  File "PYGOLANG/golang/testprog/golang_test_defer_excchain.py", line 35, in d3
    E               -    raise RuntimeError("d3: bbb")
    E               -RuntimeError: d3: bbb
    E               +Traceback (most recent call last):
    E               +  File "PYGOLANG/golang/__init__.py", line 106, in _
    E               +    return f(*argv, **kw)
    E               +  File "PYGOLANG/golang/testprog/golang_test_defer_excchain.py", line 42, in main
    E               +    raise RuntimeError("err")
    E               +RuntimeError: err
    E               +
    E               +During handling of the above exception, another exception occurred:
    E               +
    E               +Traceback (most recent call last):
    E               +  File "PYGOLANG/golang/__init__.py", line 183, in __exit__
    E               +    d()
    E               +  File "PYGOLANG/golang/testprog/golang_test_defer_excchain.py", line 31, in d1
    E               +    raise RuntimeError("d1: aaa")
    E               +RuntimeError: d1: aaa
    E               +
    E               +During handling of the above exception, another exception occurred:
    E               +
    E               +Traceback (most recent call last):
    E               +  File "PYGOLANG/golang/__init__.py", line 183, in __exit__
    E               +    d()
    E               +  File "PYGOLANG/golang/testprog/golang_test_defer_excchain.py", line 33, in d2
    E               +    1/0
    E               +ZeroDivisionError: division by zero
    E               +
    E               +During handling of the above exception, another exception occurred:
    E               +
    E               +Traceback (most recent call last):
    E               +  File "PYGOLANG/golang/testprog/golang_test_defer_excchain.py", line 45, in <module>
    E               +    main()
    E               +  File "Z:\home\kirr\src\tools\go\pygo-win\1.wenv\lib\site-packages/decorator.py", line 232, in fun
    E               +    return caller(func, *(extras + args), **kw)
    E               +  File "PYGOLANG/golang/__init__.py", line 105, in _
    E               +    with __goframe__:
    E               +  File "PYGOLANG/golang/__init__.py", line 182, in __exit__
    E               +    with __goframe__:
    E               +  File "PYGOLANG/golang/__init__.py", line 182, in __exit__
    E               +    with __goframe__:
    E               +  File "PYGOLANG/golang/__init__.py", line 183, in __exit__
    E               +    d()
    E               +  File "PYGOLANG/golang/testprog/golang_test_defer_excchain.py", line 35, in d3
    E               +    raise RuntimeError("d3: bbb")
    E               +RuntimeError: d3: bbb

Else on Windows e.g. test_defer_excchain_traceback fails as

    E           Failed: not equal:
    E           Differences (unified diff with -expected +actual):
    E               @@ -1,8 +1,8 @@
    E                Traceback (most recent call last):
    E               -  File "PYGOLANG/golang/golang_test.py", line ..., in test_defer_excchain_traceback
    E               +  File "PYGOLANG\golang\golang_test.py", line 1524, in test_defer_excchain_traceback
    E                    alpha()
    E               -  File "PYGOLANG/golang/golang_test.py", line ..., in alpha
    E               +  File "PYGOLANG\golang\golang_test.py", line 1521, in alpha
    E                    beta()
    E               -  File "PYGOLANG/golang/golang_test.py", line ..., in beta
    E               +  File "PYGOLANG\golang\golang_test.py", line 1520, in beta
    E                    raise RuntimeError("gamma")
    E                RuntimeError: gamma

Else it fails to import on Windows:

    collecting ... 05c8:err:module:import_dll Library libgolang.dll (which is needed by L"Z:\\home\\kirr\\src\\tools\\go\\pygo-win\\pygolang\\golang\\_golang.cp310-win_amd64.pyd") not found
    collected 0 items / 1 error

    =========================================================== ERRORS ===========================================================
    ___________________________________________ ERROR collecting golang/golang_test.py ___________________________________
    ImportError while importing test module 'Z:\home\kirr\src\tools\go\pygo-win\pygolang\golang\golang_test.py'.
    Hint: make sure your test modules/packages have valid Python names.
    Traceback:
    C:\Program Files\Python310\lib\importlib\__init__.py:126: in import_module
        return _bootstrap._gcd_import(name[level:], package, level)
    golang\__init__.py:45: in <module>
        from golang._golang import _pysys_exc_clear as _sys_exc_clear
    E   ImportError: DLL load failed while importing _golang: Модуль не найден.

We need to increase required setuptools_dso version because dylink_prepare_dso
and generation of *_dsoinfo.py modules was done after setuptools_dso 2.

On Windows this files are generated when linking alongside *.dll files
if there are exported symbols.

See also https://github.com/mdavidsaver/setuptools_dso/pull/25.

Libpyxruntime by definition contains python-specific code and we already
compile it with include path having python includes in it. However on
windows pyconfig.h contains

    #pragma comment(lib,"python3.lib")

which instructs the linker to automatically link to that library. And
without proper library path the link fails:

    Z:\home\kirr\src\tools\go\pygo-win\BuildTools\vc\tools\msvc\14.35.32215\bin\Hostx64\x64\link.exe /nologo /INCREMENTAL:NO /LTCG /DLL /MANIFEST:EMBED,ID=2 /MANIFESTUAC:NO /LIBPATH:build\lib.win-amd64-cpython-31
    0\golang\runtime /LIBPATH:z:\home\kirr\src\tools\go\pygo-win\BuildTools\vc\tools\msvc\14.35.32215\lib\x64 /LIBPATH:z:\home\kirr\src\tools\go\pygo-win\BuildTools\kits\10\lib\10.0.22000.0\ucrt\x64 /LIBPATH:z:\h
    ome\kirr\src\tools\go\pygo-win\BuildTools\kits\10\lib\10.0.22000.0\um\x64 libgolang.lib build\temp.win-amd64-cpython-310\Release\golang/runtime/libpyxruntime.obj /OUT:build\lib.win-amd64-cpython-310\golang\ru
    ntime\libpyxruntime.dll /IMPLIB:build\lib.win-amd64-cpython-310\golang\runtime\libpyxruntime.lib
    LINK : fatal error LNK1104: cannot open file 'python310.lib'

-> Fix it by providing proper library path for python.dll .

We need to do it ourselves only for libpyxruntime dso because for py
extensions this is automatically done by distutils out of the box.

On Windows rthere is no fcntl

    golang/runtime\_runtime_gevent.cpp(4811): error C3861: 'S_ISBLK': identifier not found
    golang/runtime\_runtime_gevent.cpp(4823): error C2039: 'Fcntl': is not a member of 'golang::internal::syscall'
    .\golang/runtime/internal/syscall.h(36): note: see declaration of 'golang::internal::syscall'
    golang/runtime\_runtime_gevent.cpp(4823): error C2065: 'F_GETFL': undeclared identifier
    golang/runtime\_runtime_gevent.cpp(4823): error C3861: 'Fcntl': identifier not found
    golang/runtime\_runtime_gevent.cpp(4870): error C2065: 'O_ACCMODE': undeclared identifier
    golang/runtime\_runtime_gevent.cpp(4889): error C2039: 'Fcntl': is not a member of 'golang::internal::syscall'
    .\golang/runtime/internal/syscall.h(36): note: see declaration of 'golang::internal::syscall'
    golang/runtime\_runtime_gevent.cpp(4889): error C2065: 'F_SETFL': undeclared identifier
    golang/runtime\_runtime_gevent.cpp(4889): error C2065: 'O_NONBLOCK': undeclared identifier
    golang/runtime\_runtime_gevent.cpp(4889): error C3861: 'Fcntl': identifier not found

and even if there would be gevent does not provide cooperative version
of FileObject for non-POSIX platforms.

-> Always use FileObjectThread on windows even for pipes.

There is no fcntl on windows. Named pipes can be set into nonblocking
mode via SetNamedPipeHandleState(PIPE_NOWAIT).

On MSVC there is no sigaction and we have to use signal. Fortunately
our sigaction usage in os/signal can be practically emulated because we
do not use all features of sigaction and because on MSVC there is
SIG_GET signal extension to query current signal handler without
resetting it.

Because the emulation is limited we keep it in os/signal.cpp instead of
adjusting syscall::Sigaction .

On MSVC we will need to use signal(2), because there is no sigaction,
and sigaction will be partly emulated through that. Move signal setting
code into common place as a preparatory step.

- there is no strerror_r, but strerror_s instead
- fcntl is not supported
- we need to explicitly tell open to open files in binary mode
- pipes are created via _pipe and explicitly in binary mode
- there is no sigaction.

This way e.g. O_CLOEXEC can be passed in at pipe creation time removing
potential race in between pipe+fcntl vs exec in the middle. It will also
help in windows porting in follow-up patches becuase there is no fcntl
on Windows, but pipe with O_CLOEXEC semantic can be created directly
with flags=_O_NOINHERIT.

There is no fork on windows and that we do not need to install atfork
handler at all.

    golang/runtime/internal/atomic.cpp(23): fatal error C1083: Cannot open include file: 'pthread.h': No such file or directory

- there is no __attribute__ on that compiler
- sadly va_start is rejected to work on reference:

    z:\home\kirr\src\tools\go\pygo-win\BuildTools\vc\tools\msvc\14.35.32215\include\vadefs.h(194): error C2338: static_assert failed: 'va_start argument must not have reference type and must not be parenthesized'
    golang/fmt.cpp(53): note: see reference to class template instantiation '__vcrt_assert_va_start_is_not_reference<const golang::string &>' being compiled

  -> change format from string& to be string in sprintf.

  Probably it should be ok in practice from performance point of view because
  string contains only pointer to data, not the data itself.

- There is no S_IRUSR & friends  -> use _S_IREAD & co.
- Tthere is no sys_siglist       -> kind-of define it ourselves for all documented signals.

list_entry, as provided by linux/list.h, uses statement expressions(*) which
are not supported by MSVC:

    #define list_entry(ptr, type, member) ({              \
            const typeof( ((type *)0)->member ) *__mptr = (ptr);   \
            (type *)( (char *)__mptr - offsetof(type,member) );})

    golang/runtime/libgolang.cpp(439): error C2059: syntax error: '{'
    golang/runtime/libgolang.cpp(439): error C2143: syntax error: missing ';' before '{'
    golang/runtime/libgolang.cpp(439): error C4430: missing type specifier - int assumed. Note: C++ does not support default-int
    golang/runtime/libgolang.cpp(439): error C2440: 'initializing': cannot convert from 'list_head' to 'int'
    golang/runtime/libgolang.cpp(439): note: No user-defined-conversion operator available that can perform this conversion, or the operator cannot be called
    golang/runtime/libgolang.cpp(439): error C2143: syntax error: missing ';' before '*'
    golang/runtime/libgolang.cpp(439): error C2065: '__mptr': undeclared identifier
    golang/runtime/libgolang.cpp(439): error C2059: syntax error: ')'

-> work it around by defining list_entry with C++ lambda.

(*) https://gcc.gnu.org/onlinedocs/gcc/Statement-Exprs.html

There is no std::random_shuffle on `MSVC /std:c++20` because it was removed in C++17:

    golang/runtime/libgolang.cpp(946): error C2039: 'random_shuffle': is not a member of 'std'
    z:\home\kirr\src\tools\go\pygo-win\BuildTools\vc\tools\msvc\14.35.32215\include\random(34): note: see declaration of 'std'
    golang/runtime/libgolang.cpp(946): error C3861: 'random_shuffle': identifier not found

    https://en.cppreference.com/w/cpp/algorithm/random_shuffle

We need unistd.h because e.g. `cimport posix.stat` forces inclusion of unistd.h
even if we use part of posix.stat that is available everywhere.

We use bzero in libgolang.cpp - provide it in similar way via compat
strings.h because on windows there is only string.h (no "s" in the end).

We also use mode_t in several places - provide it via typedef in
libgolang.h directly, because fcntl.h is present on MSVC.

MSVC does not accept -std=c++11 but instead accepts /std:c++11. We cannot
use that however because with /std:c++11 compilation fails with

    .\golang/libgolang.h(280): error C7555: use of designated initializers requires at least '/std:c++20'
    .\golang/libgolang.h(294): error C7555: use of designated initializers requires at least '/std:c++20'
    .\golang/libgolang.h(308): error C7555: use of designated initializers requires at least '/std:c++20'

for

    276 // _selsend creates `_chansend(ch, ptx)` case for _chanselect.
    277 static inline
    278 _selcase _selsend(_chan *ch, const void *ptx) {
    279     _selcase _ = {
    280         .ch     = ch,			<-- NOTE
    281         .op     = _CHANSEND,
    282         .flags  = (enum _selflags)0,
    283         .user   = 0xff,
    284     };

and similar places.

-> Use /std:c++20 instead as MSVC advices  (WOW designated initializers are C99
and it took 21 years for C++ to catch up).

We also need to adjust exception handling mode into "fully conformant" instead
of "assume extern C cannot throw" setuptools default so that `panic` and other
extern C libgolang functions generate exceptions that could be caught
instead of crashing programs.

For C vs C++ flags we also need to adjust our build_ext, because the way
setuptools/distutils organize compilation for MSVC is different from
UNIX compilers.

We already reuse golang.pyx.build in setup.py to build Extensions, but
DSOs were built via setuptools_dso directly so far. To support Windows
we will soon need to adjust compilation flags for both Extensions and
DSOs. It makes sense to first concentrate build recipes in one place
before doing that.

-> Move/factor DSOs build flags into golang.pyx.build and reuse that
from setup.

We already try to annotate functions exported from DSOs as such.
However so far we were testing only on Linux and macOS where
-fvisibility=hidden is not the default, and thus linker forgives us
annotation mistakes. But on Windows the default is to have hidden
visibility out of the box and so the linker becomes strict about this.

-> Fix all issues caught there.

For example here is how it breaks if ~_interface() is not annotated properly:

    building 'golang.runtime.libpyxruntime' DSO as build\lib.win-amd64-cpython-310\golang\runtime\libpyxruntime.dll
    ...
    Z:\home\kirr\src\tools\go\pygo-win\BuildTools\vc\tools\msvc\14.35.32215\bin\Hostx64\x64\link.exe /nologo /INCREMENTAL:NO /LTCG /DLL /MANIFEST:EMBED,ID=2 /MANIFESTUAC:NO "/LIBPATH:C:\Program Files\Python310\li
    bs" /LIBPATH:build\lib.win-amd64-cpython-310\golang\runtime /LIBPATH:z:\home\kirr\src\tools\go\pygo-win\BuildTools\vc\tools\msvc\14.35.32215\lib\x64 /LIBPATH:z:\home\kirr\src\tools\go\pygo-win\BuildTools\kits
    \10\lib\10.0.22000.0\ucrt\x64 /LIBPATH:z:\home\kirr\src\tools\go\pygo-win\BuildTools\kits\10\lib\10.0.22000.0\um\x64 libgolang.lib build\temp.win-amd64-cpython-310\Release\golang/runtime/libpyxruntime.obj /OU
    T:build\lib.win-amd64-cpython-310\golang\runtime\libpyxruntime.dll /IMPLIB:build\lib.win-amd64-cpython-310\golang\runtime\libpyxruntime.lib
       Creating library build\lib.win-amd64-cpython-310\golang\runtime\libpyxruntime.lib and object build\lib.win-amd64-cpython-310\golang\runtime\libpyxruntime.exp

    libpyxruntime.obj : error LNK2001: unresolved external symbol "protected: __cdecl golang::_interface::~_interface(void)" (??1_interface@golang@@IEAA@XZ)
    build\lib.win-amd64-cpython-310\golang\runtime\libpyxruntime.dll : fatal error LNK1120: 1 unresolved externals
    error: command 'Z:\\home\\kirr\\src\\tools\\go\\pygo-win\\BuildTools\\vc\\tools\\msvc\\14.35.32215\\bin\\Hostx64\\x64\\link.exe' failed with exit code 1120

    (z-dev) kirr@deca:~/src/tools/go/pygolang$ check-manifest
    lists of files in version control and sdist do not match!
    missing from VCS:
      golang/pyx/runtime.cpp
      golang/runtime/libgolang_dsoinfo.py
      golang/runtime/libpyxruntime_dsoinfo.py

- golang/pyx/runtime.cpp is generated from golang/pyx/runtime.pyx
- *_dsoinfo.py files are generated by setuptools_dso during the build

Tests now pass with those versions.
Remove py38-dbg from test matrix ad this version is now a bit outdated
and having just py38 without dbg there seems enough.

I forgot to add py38 and py39 here while adding them in 792cbd6c (tox:
-py36,py37d  +py38d, py38) and 32167853 (tox += CPython3.9). The former
commit also removed py37d from test matrix.

Python changed traceback output a bit:

- added '^^^^^^^' and '~~^~~'
- changed lineno of frame corresponding to __exit__ to be at line of `with ...`

-> Adjust to that by introducing a bit more generalized conditionals in
   assertDoc.

Here is, for example, how test_defer_excchain_traceback was failing on py3.11:

E           Failed: not equal:
E           Differences (unified diff with -expected +actual):
E               @@ -1,6 +1,7 @@
E                Traceback (most recent call last):
E               -  File "PYGOLANG/golang/__init__.py", line ..., in _
E               +  File "PYGOLANG/golang/__init__.py", line 103, in _
E                    return f(*argv, **kw)
E               -  File "PYGOLANG/golang/golang_test.py", line ..., in caller
E               +           ^^^^^^^^^^^^^^
E               +  File "PYGOLANG/golang/golang_test.py", line 1550, in caller
E                    raise RuntimeError("ccc")
E                RuntimeError: ccc
E               @@ -9,7 +10,7 @@
E                <BLANKLINE>
E                Traceback (most recent call last):
E               -  File "PYGOLANG/golang/__init__.py", line ..., in __exit__
E               +  File "PYGOLANG/golang/__init__.py", line 180, in __exit__
E                    d()
E               -  File "PYGOLANG/golang/golang_test.py", line ..., in q2
E               +  File "PYGOLANG/golang/golang_test.py", line 1548, in q2
E                    raise RuntimeError("bbb")
E                RuntimeError: bbb
E               @@ -18,14 +19,16 @@
E                <BLANKLINE>
E                Traceback (most recent call last):
E               -  File "PYGOLANG/golang/golang_test.py", line ..., in test_defer_excchain_traceback
E               +  File "PYGOLANG/golang/golang_test.py", line 1553, in test_defer_excchain_traceback
E                    caller()
E               -  ...
E               -  File "PYGOLANG/golang/__init__.py", line ..., in _
E               -    return f(*argv, **kw)
E               -  File "PYGOLANG/golang/__init__.py", line ..., in __exit__
E               +  File "/home/kirr/src/tools/go/py3.venv/lib/python3.11/site-packages/decorator.py", line 232, in fun
E               +    return caller(func, *(extras + args), **kw)
E               +           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
E               +  File "PYGOLANG/golang/__init__.py", line 102, in _
E               +    with __goframe__:
E               +  File "PYGOLANG/golang/__init__.py", line 179, in __exit__
E               +    with __goframe__:
E               +  File "PYGOLANG/golang/__init__.py", line 180, in __exit__
E                    d()
E               -  File "PYGOLANG/golang/__init__.py", line ..., in __exit__
E               -    d()
E               -  File "PYGOLANG/golang/golang_test.py", line ..., in q1
E               +  File "PYGOLANG/golang/golang_test.py", line 1545, in q1
E                    raise RuntimeError("aaa")
E                RuntimeError: aaa

IPython8 changed format of output tracebacks (see
https://github.com/ipython/ipython/commit/02660f35 and further). Adding
test support for later versions would add maintenance cost on pygolang
side, but testing this is actually not needed, since we activate
IPython-related patch only on py2 and for py2 the latest ipython version
is ipython5.

-> So simply skip this test if we see we have IPython ≥ 8.
   Skip it only on py3 just in case.

For the reference here is how diff in between running
golang_test_defer_excchain.py on IPython7 and IPython8 looks:

    diff --git a/golang/testprog/7 b/golang/testprog/8
    index 5c31ed2..8fea57b 100644
    --- a/golang/testprog/7
    +++ b/golang/testprog/8
    @@ -1,101 +1,91 @@
    -[22;0t]0;IPython: golang/testprog---------------------------------------------------------------------------
    +---------------------------------------------------------------------------
     RuntimeError                              Traceback (most recent call last)
    -~/src/tools/go/pygolang-master/golang/__init__.py in _(f, *argv, **kw)
    -    102         with __goframe__:
    ---> 103             return f(*argv, **kw)
    -    104
    +File ~/src/tools/go/pygolang-master/golang/__init__.py:103, in _func.<locals>._(f, *argv, **kw)
    +    102 with __goframe__:
    +--> 103     return f(*argv, **kw)

    -~/src/tools/go/pygolang-master/golang/testprog/golang_test_defer_excchain.py in main()
    -     41     defer(d1)
    ----> 42     raise RuntimeError("err")
    -     43
    +File ~/src/tools/go/pygolang-master/golang/testprog/golang_test_defer_excchain.py:42, in main()
    +     41 defer(d1)
    +---> 42 raise RuntimeError("err")

     RuntimeError: err

     During handling of the above exception, another exception occurred:

     RuntimeError                              Traceback (most recent call last)
    -~/src/tools/go/pygolang-master/golang/__init__.py in __exit__(__goframe__, exc_type, exc_val, exc_tb)
    -    179             with __goframe__:
    ---> 180                 d()
    -    181
    +File ~/src/tools/go/pygolang-master/golang/__init__.py:180, in _GoFrame.__exit__(__goframe__, exc_type, exc_val, exc_tb)
    +    179     with __goframe__:
    +--> 180         d()
    +    182 return __goframe__.recovered

    -~/src/tools/go/pygolang-master/golang/testprog/golang_test_defer_excchain.py in d1()
    +File ~/src/tools/go/pygolang-master/golang/testprog/golang_test_defer_excchain.py:31, in d1()
          30 def d1():
     ---> 31     raise RuntimeError("d1: aaa")
    -     32 def d2():

     RuntimeError: d1: aaa

     During handling of the above exception, another exception occurred:

     ZeroDivisionError                         Traceback (most recent call last)
    -~/src/tools/go/pygolang-master/golang/__init__.py in __exit__(__goframe__, exc_type, exc_val, exc_tb)
    -    179             with __goframe__:
    ---> 180                 d()
    -    181
    +File ~/src/tools/go/pygolang-master/golang/__init__.py:180, in _GoFrame.__exit__(__goframe__, exc_type, exc_val, exc_tb)
    +    179     with __goframe__:
    +--> 180         d()
    +    182 return __goframe__.recovered

    -~/src/tools/go/pygolang-master/golang/testprog/golang_test_defer_excchain.py in d2()
    +File ~/src/tools/go/pygolang-master/golang/testprog/golang_test_defer_excchain.py:33, in d2()
          32 def d2():
     ---> 33     1/0
    -     34 def d3():

     ZeroDivisionError: division by zero

     During handling of the above exception, another exception occurred:

     RuntimeError                              Traceback (most recent call last)
    -/usr/lib/python3.11/runpy.py in run_module(mod_name, init_globals, run_name, alter_sys)
    +File <frozen runpy>:226, in run_module(mod_name, init_globals, run_name, alter_sys)

    -/usr/lib/python3.11/runpy.py in _run_module_code(code, init_globals, mod_name, mod_spec, pkg_name, script_name)
    +File <frozen runpy>:98, in _run_module_code(code, init_globals, mod_name, mod_spec, pkg_name, script_name)

    -/usr/lib/python3.11/runpy.py in _run_code(code, run_globals, init_globals, mod_name, mod_spec, pkg_name, script_name)
    +File <frozen runpy>:88, in _run_code(code, run_globals, init_globals, mod_name, mod_spec, pkg_name, script_name)

    -~/src/tools/go/pygolang-master/golang/testprog/golang_test_defer_excchain.py in <module>
    -     43
    +File ~/src/tools/go/pygolang-master/golang/testprog/golang_test_defer_excchain.py:45
    +     42     raise RuntimeError("err")
          44 if __name__ == "__main__":
     ---> 45     main()

    -~/src/tools/go/py3.venv/lib/python3.11/site-packages/decorator.py in fun(*args, **kw)
    -    230             if not kwsyntax:
    -    231                 args, kw = fix(args, kw, sig)
    ---> 232             return caller(func, *(extras + args), **kw)
    -    233     fun.__name__ = func.__name__
    -    234     fun.__doc__ = func.__doc__
    +File ~/src/tools/go/py3.venv/lib/python3.11/site-packages/decorator.py:232, in decorate.<locals>.fun(*args, **kw)
    +    230 if not kwsyntax:
    +    231     args, kw = fix(args, kw, sig)
    +--> 232 return caller(func, *(extras + args), **kw)

    -~/src/tools/go/pygolang-master/golang/__init__.py in _(f, *argv, **kw)
    -    100         # run f under separate frame, where defer will register calls.
    -    101         __goframe__ = _GoFrame()
    ---> 102         with __goframe__:
    -    103             return f(*argv, **kw)
    -    104
    +File ~/src/tools/go/pygolang-master/golang/__init__.py:102, in _func.<locals>._(f, *argv, **kw)
    +     99 def _(f, *argv, **kw):
    +    100     # run f under separate frame, where defer will register calls.
    +    101     __goframe__ = _GoFrame()
    +--> 102     with __goframe__:
    +    103         return f(*argv, **kw)

    -~/src/tools/go/pygolang-master/golang/__init__.py in __exit__(__goframe__, exc_type, exc_val, exc_tb)
    -    177
    -    178             # even if d panics - we have to call other defers
    ---> 179             with __goframe__:
    -    180                 d()
    -    181
    +File ~/src/tools/go/pygolang-master/golang/__init__.py:179, in _GoFrame.__exit__(__goframe__, exc_type, exc_val, exc_tb)
    +    176     d = __goframe__.deferv.pop()
    +    178     # even if d panics - we have to call other defers
    +--> 179     with __goframe__:
    +    180         d()
    +    182 return __goframe__.recovered

    -~/src/tools/go/pygolang-master/golang/__init__.py in __exit__(__goframe__, exc_type, exc_val, exc_tb)
    -    177
    -    178             # even if d panics - we have to call other defers
    ---> 179             with __goframe__:
    -    180                 d()
    -    181
    +File ~/src/tools/go/pygolang-master/golang/__init__.py:179, in _GoFrame.__exit__(__goframe__, exc_type, exc_val, exc_tb)
    +    176     d = __goframe__.deferv.pop()
    +    178     # even if d panics - we have to call other defers
    +--> 179     with __goframe__:
    +    180         d()
    +    182 return __goframe__.recovered

    -~/src/tools/go/pygolang-master/golang/__init__.py in __exit__(__goframe__, exc_type, exc_val, exc_tb)
    -    178             # even if d panics - we have to call other defers
    -    179             with __goframe__:
    ---> 180                 d()
    -    181
    -    182         return __goframe__.recovered
    +File ~/src/tools/go/pygolang-master/golang/__init__.py:180, in _GoFrame.__exit__(__goframe__, exc_type, exc_val, exc_tb)
    +    178     # even if d panics - we have to call other defers
    +    179     with __goframe__:
    +--> 180         d()
    +    182 return __goframe__.recovered

    -~/src/tools/go/pygolang-master/golang/testprog/golang_test_defer_excchain.py in d3()
    -     33     1/0
    +File ~/src/tools/go/pygolang-master/golang/testprog/golang_test_defer_excchain.py:35, in d3()
          34 def d3():
     ---> 35     raise RuntimeError("d3: bbb")
    -     36
    -     37 @func

     RuntimeError: d3: bbb

Starting from python3.11 inspect.formatargspec was removed:

    f = <function test_func.<locals>.zzz at 0x7fb6d265fec0>

        def fmtargspec(f): # -> str
            with warnings.catch_warnings():
                warnings.simplefilter('ignore', DeprecationWarning)
    >           return inspect.formatargspec(*inspect.getargspec(f))
    E           AttributeError: module 'inspect' has no attribute 'formatargspec'

    golang/golang_test.py:1823: AttributeError

We were already handling formatargspec deprecation in 45f4df9e (golang:
tests: Silence inspect deprecation warning), but now is the time to
actually replace its usage.

-> Fix it by using `str(inspect.signature(f))` instead of
   `inspect.formatargspec(*inspect.getargspec(f))`.

With setuptools 65 running test_pyx_build_cmdclass is failing because besides
cmdclass_custom.py it sees nearby golang_pyx_user/ and golang_dso_user/ with
top-project setups and rejects it:

    ---- 8< ----
    golang/pyx/build_test.py::test_pyx_build_cmdclass error: Multiple top-level packages discovered in a flat-layout: ['golang_pyx_user', 'golang_dso_user'].

    To avoid accidental inclusion of unwanted files or directories,
    setuptools will not proceed with this build.

    If you are trying to create a single distribution with multiple packages
    on purpose, you should not rely on automatic discovery.
    Instead, consider the following options:

    1. set up custom discovery (`find` directive with `include` or `exclude`)
    2. use a `src-layout`
    3. explicitly set `py_modules` or `packages` with a list of names

    To find more information, look for "package discovery" on setuptools docs.
    FAILED

    ================================ FAILURES =================================
    _________________________ test_pyx_build_cmdclass _________________________

        def test_pyx_build_cmdclass():
    >       _ = pyout(["cmdclass_custom.py", "build_ext"], cwd=testprog)

    golang/pyx/build_test.py:60:
    _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
    golang/golang_test.py:1742: in pyout
        return pyrun(argv, stdin=stdin, stdout=stdout, stderr=stderr, **kw)
    _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

    argv = ['cmdclass_custom.py', 'build_ext'], stdin = None, stdout = b'', stderr = None
    kw = {'cwd': '/home/kirr/src/tools/go/pygolang-master/golang/pyx/testprog'}, retcode = 1

        def pyrun(argv, stdin=None, stdout=None, stderr=None, **kw):
            retcode, stdout, stderr = _pyrun(argv, stdin=stdin, stdout=stdout, stderr=stderr, **kw)
            if retcode:
    >           raise RuntimeError(' '.join(argv) + '\n' + (stderr and str(stderr) or '(failed)'))
    E           RuntimeError: cmdclass_custom.py build_ext
    E           (failed)

    golang/golang_test.py:1736: RuntimeError
    ---- 8< ----

-> Work it around by defining py_modules explicitly as suggested in
https://stackoverflow.com/a/72547402/9456786.

We use &vector[0] in several places to get the pointer to vector data,
but std::vector[i] states invariant that i must be < vector.size(). If
the vector is not empty - then &vector[0] works ok. However if the
vector is empty - then the invariant is broken.

Normally it should not be a problem, since with empty vector we usually
use (&vector[0], vector.size()) pair, and for empty vector its size is
zero. In other words even if &vector[0] returns some not good pointer
with zero size that data should never be accessed. But a build of
libstdc++ could have asserts turned on and verify that i is actually <
size. For example with default install on Fedora the following program
with plain select()

    from golang import select
    select()

crashes with assert triggered on the breakage of that invariant

    [Thread debugging using libthread_db enabled]
    Using host libthread_db library "/lib64/libthread_db.so.1".
    /usr/include/c++/10/bits/stl_vector.h:1042: std::vector<_Tp, _Alloc>::reference std::vector<_Tp, _Alloc>::operator[](std::vector<_Tp, _Alloc>::size_type) [with _Tp = golang::_selcase; _Alloc = std::allocator<golang::_selcase>; std::vector<_Tp, _Alloc>::reference = golang::_selcase&; std::vector<_Tp, _Alloc>::size_type = long unsigned int]: Assertion '__builtin_expect(__n < this->size(), true)' failed.

    Program received signal SIGABRT, Aborted.
    0x00007ffff7e22a25 in raise () from /lib64/libc.so.6
    (gdb) bt
    #0  0x00007ffff7e22a25 in raise () from /lib64/libc.so.6
    #1  0x00007ffff7e0b895 in abort () from /lib64/libc.so.6
    #2  0x00007fffea638d6d in std::__replacement_assert (__condition=0x7fffea63ea88 "__builtin_expect(__n < this->size(), true)",
        __function=0x7fffea63eab8 "std::vector<_Tp, _Alloc>::reference std::vector<_Tp, _Alloc>::operator[](std::vector<_Tp, _Alloc>::size_type) [with _Tp = golang::_selcase; _Alloc = std::allocator<golang::_selcase>; std::vector<_Tp, "..., __line=1042, __file=0x7fffea63ebe8 "/usr/include/c++/10/bits/stl_vector.h")
        at /usr/include/c++/10/x86_64-redhat-linux/bits/c++config.h:2552
    #3  std::vector<golang::_selcase, std::allocator<golang::_selcase> >::operator[] (this=<synthetic pointer>, __n=0)
        at /usr/include/c++/10/bits/stl_vector.h:1042
    #4  std::vector<golang::_selcase, std::allocator<golang::_selcase> >::operator[] (__n=0, this=<synthetic pointer>)
        at /usr/include/c++/10/bits/stl_vector.h:1040
    #5  __pyx_pf_6golang_7_golang_6pyselect (__pyx_self=<optimized out>, __pyx_v_pycasev=<optimized out>) at golang/_golang.cpp:7930
    #6  __pyx_pw_6golang_7_golang_7pyselect (__pyx_self=<optimized out>, __pyx_args=<optimized out>, __pyx_kwds=<optimized out>) at golang/_golang.cpp:7284
    #7  0x00007ffff7bceeab in cfunction_call_varargs (func=<built-in function pyselect>, args=(), kwargs=0x0)
        at /usr/src/debug/python3-3.8.10-1.fc32.x86_64/Objects/call.c:743
    ...

-> Fix it all via replacing &vector[0] with vector.data() everywhere.

No need to add new test since select() is used by test_blockforever()
and running that test on Fedora was crashing as well.

/reviewed-by @jerome
/reviewed-at !22

Since the beginning (9bf03d9c "py.bench: New command to benchmark python
code similarly to `go test -bench`") py.bench was automatically
discovering benchmarks in bench_*.py files only. This was inherited from
wendelin.core which keeps its benchmarks in those files.

However in pygolang, following Go convention(*), we already have several
benchmarks that reside together with tests in same *_test.py files. And
currently just running py.bench does not discover them.

-> Let's fix this and teach py.bench to automatically discover
benchmarks in the test files by default as well.

Pytest's default is to look for tests in test_*.py and *_test.py (+).
Add those patterns and also keep bench_*.py for backward compatibility.

Before this patch running py.bench inside pygolang repository does not
run any benchmark at all. After the patch py.bench runs all the
benchmarks by default:

    (z-dev) kirr@deca:~/src/tools/go/pygolang$ py.bench
    ========================= test session starts ==========================
    platform linux2 -- Python 2.7.18, pytest-4.6.11, py-1.10.0, pluggy-0.13.1
    rootdir: /home/kirr/src/tools/go/pygolang
    plugins: timeout-1.4.2, profiling-1.7.0, mock-2.0.0
    collected 18 items

    pymod: golang/golang_str_test.py
    Benchmarkstddecode              2000000 0.756 µs/op
    Benchmarkudecode                20000   74.359 µs/op
    Benchmarkstdencode              3000000 0.327 µs/op
    Benchmarkbencode                40000   32.613 µs/op

    pymod: golang/golang_test.py
    Benchmarkpyx_select_nogil       500000  2.051 µs/op
    Benchmarkpyx_go_nogil           90000   12.177 µs/op
    Benchmarkpyx_chan_nogil         600000  1.826 µs/op
    Benchmarkgo                     80000   13.267 µs/op
    Benchmarkchan                   500000  2.076 µs/op
    Benchmarkselect                 300000  3.835 µs/op
    Benchmarkdef                    30000000        0.035 µs/op
    Benchmarkfunc_def               40000   29.387 µs/op
    Benchmarkcall                   30000000        0.043 µs/op
    Benchmarkfunc_call              2000000 0.819 µs/op
    Benchmarktry_finally            20000000        0.096 µs/op
    Benchmarkdefer                  600000  1.755 µs/op

    pymod: golang/sync_test.py
    Benchmarkworkgroup_empty        40000   25.807 µs/op
    Benchmarkworkgroup_raise        40000   31.637 µs/op                     [100%]

    =========================== warnings summary ===========================

(*) see https://pkg.go.dev/cmd/go#hdr-Test_packages
(+) see https://docs.pytest.org/en/7.1.x/reference/reference.html#confval-python_files

/reviewed-by @jerome
/reviewed-on !20

We recently moved our custom UTF-8 encoding/decoding routines to Cython.
Now we can start taking speedup advantage on C level to make our own
UTF-8 decoder a bit less horribly slow on py2:

    name       old time/op  new time/op  delta
    stddecode   752ns ± 0%   743ns ± 0%   -1.19%  (p=0.000 n=9+10)
    udecode     216µs ± 0%    75µs ± 0%  -65.19%  (p=0.000 n=9+10)
    stdencode   328ns ± 2%   327ns ± 1%     ~     (p=0.252 n=10+9)
    bencode    34.1µs ± 1%  32.1µs ± 1%   -5.92%  (p=0.000 n=10+10)

So it is ~ 3x speedup for u(), but still significantly slower compared
to std unicode.decode('utf-8').

Only low-hanging fruit here to make _utf_decode_rune a bit more prompt,
since it sits in the most inner loop. In the future
_utf8_decode_surrogateescape might be reworked as well to avoid
constructing resulting unicode via py-level list of py-unicode character
objects. And similarly for _utf8_encode_surrogateescape.

On py3 the performance of std and u/b decode/encode is approximately the same.

/trusted-by @jerome
/reviewed-on nexedi/pygolang!19

Error rune (u+fffd) is returned by _utf8_decode_rune to indicate an
error in decoding. But the error rune itself is valid unicode codepoint:

   >>> x = u"�"
   >>> x
   u'\ufffd'
   >>> x.encode('utf-8')
   '\xef\xbf\xbd'

This way only (r=_rune_error, size=1) should be treated by the caller as
utf8 decoding error.

But e.g. strconv.quote was not careful to also inspect the size, and this way
was quoting � into just "\xef" instead of "\xef\xbf\xbd".
_utf8_decode_surrogateescape was also subject to similar error.

-> Fix it.

Without the fix e.g. added test for strconv.quote fails as

    >           assert quote(tin) == tquoted
    E           assert '"\xef"' == '"�"'
    E             - "\xef"
    E             + "�"

/reviewed-by @jerome
/reviewed-at !18